In English orthography there are no rules, only tendencies!
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StoneyBAug 16 '12 at 12:53

1

Why is "service" pronounced so much like "crevice" – is that what you're asking?
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J.R.Aug 16 '12 at 13:15

4

"I would think that if they end the same way, the same pronunciation rules should apply as well." Just like head and bead? Or bough, cough, rough, though, and through? It's hard to make that kind of assertion about a language that gives us the likes of live and live, read and read, and wind and wind.
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J.R.Aug 16 '12 at 13:30

"the same pronunciation rules" I don't think we generally have pronunciation rules in English. Spellings were normally made to represent pronunciations, rather than the other way around.
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bdslDec 28 '14 at 20:04

I can't speak to the history, and I'm not an OF scholar, so I can't say what stress, if any, the words had before they migrated across the Channel. But certainly anyone who used the words would be aware that the orthographic identity of the endings is accidental: service is serv- with a suffix, device is vis- with a prefix. That sets the stress, after which the GVS takes over.
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StoneyBAug 16 '12 at 12:50

This has less to do with GVS, more to do with stress, as John Lawler described.
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RainDoctorAug 16 '12 at 17:59

Well I think it has to do with both, the sounds used to be the same (length excepted) and diverged during the GVS because one was stressed and the other was not.
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Julien Ch.Aug 17 '12 at 7:05

It's entirely a matter of syllable stress. English is a stress-timed language. Only a stressed syllable can have a full vowel in English; unstressed syllables are centralized and reduced as much as possible, especially in rapid speech.

SERvice is stressed on the first syllable, so the vowel in the first syllable gets fully pronounced ['sɝ], while the second unstressed syllable is reduced to shwa [vəs].

On the hand, deVICE is stressed on the second syllable, so the vowel in that syllable gets fully pronounced ['vəys], while the first unstressed syllable is reduced to shwa [də].

Spelling has nothing to do with punctuation. English spelling was invented for a different language and doesn't work at all well for modern English. This fact explains a lot of other things, including why you shouldn't be worried if it's not logical. In fact, you're right. -- it's not logical.

You seem to be defining “secondary stress” as “not stressed but having unreduced vowels”, and defining “unstressed” as “not stressed and having reduced vowels”. Is that correct?
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tchristAug 16 '12 at 21:04

I'm going out on a limb a little but, I'm fairly sure that words that have two consonants followed by "ice" are pronounced like service. Words where "ice" is preceded by a wovel and consonant are pronounced like device.

Had a look. There's only about a dozen or so of words where the letter pattern is vowel, consonant and followed by "ice." The only exception for pronunciation in this group is "sacrifice." The sixy or so words that aren't in the above group don't follow much pattern in pronunciation. I think i've proven my answer thoroughly wrong.
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ChrisAug 17 '12 at 0:31